Method and means for determining altitude



ZBEWQOO SH v XR 2,324,604 SEARCH ROOM Y 1, CROSS REFRNCE Y July 2 0, 1943. v A. svosoDA @324,504

METHOD AND MEANS FORDETSRMINING LTITUDE Filed May 1, 1941 Patented July 2G, 1943 UNITED STATES PATENT orifice l METHOD AND MEANS FOR DETERMINING ALTITUDE Antonin Svoboda, Forest Hills, N. Y., assigner to Abax Corporation, New York, N. Y., a corporation of New York Application May 1, 1941, Serial No. 391,248

In France May 3, 1940 j 5 Claims.

is constant and that the airplane is moving at a l speed that is constant in magnitude and in direction.

When an airplane is flying at a constant al` titude at a speed that is constant in magnitude and in direction, the rectangular cio-ordinates of l its horizontal projection vary as a function of the time, according to a linear law, that is to say, so that a stylus which is displaced transversely 'to the uniform movement of a recording surface, Y

proportionally to one of these co-ordinates, must trace a. straight line. One can determine the rectangular co-ordinates of a horizontal projection of the airplane from the acoustic co-ordinates by taking account of the timewhich the sound of the airplane takes to arrive at the listening station, a time which, for a xed site,v is a function of the altitude of the airplane. If a mistake is made as to the altitude of the airplane, the inexact optical co-ordinates record themselves in the form of curves which are substantially hy- 3,

perbolas.

In accordance with the invention, several styli trace simultaneously, as a function of the time, from the acoustic Cso-ordinates of the airplane, a

family of curves representing one and the same rectangular co-ordinate of the horizontal projection of the airplane, for different values at- ,t

tributed to the altitude. Among these curves,

the one which most closely approximates a y straight line corresponds to the altitude closest to it is obviously necessary that it should not stretch 5n out too muc-h in the direction of the displacement oi the record strip or, on 'the contrary, that it shall not flatten out too much.

In the apparatus in accordance Withthe invention, a speed-change mechanism inserted in 55 the control of the displacement of the record strip makes it possible to impart to this displacement the speed which is most suitable for the yorder of magnitude of the altitude to be determined. It is apparent that the speed imparted to the strip is suitable when one element of the graph is oriented appreciably at in relation to the direction of displacement of the strip.

The annexed drawing represents diagrammatically, as an example, one embodiment of an apparatus in conformity with the invention.

The apparatus illustrated has two input shafts `5 and I 6 which, in the use of the device, are

turned proportionately to the acoustic bearing and acoustic angular elevation of an airplane as indicated by any known form of listening device. The turning movements given to the two input shafts move the four sliding stylus blocks 5C through the medium of connecting mechanism hereinafter described.

On one end of a horizontal shaft I there is keyed a slottedcrank 2. On this same shaft there is mounted, so as to be idle, a disc 3. The latter has cut therein a groove Il in spiral form (ps-.K cot o', in polar co-ordinates), onhitsside which faces the slotted crank 2. The shaft l rotates proportionally to the angle of acoustic bearing Ga of the airplane. Its rotation is controlled by a shaft 5 formed of two sections between which there is interposed a differential E. The shaft 5 is connected to the shaft i by means of a pair 'l of bevel gears. A vertical shaft 8 of the differential E is intended to make it possible v to subtract from the acoustic bearing a variable angle a. It is equipped with an operating handwheel 9, bearing a pointer, which it suces t0 orient roughly by ear in the direction where one hears the airplane coming.

The acoustic bearing is likewise transmitted to Ithe disc 3fr0m the shaft l by the pair of bevel gears i0, the shaft ll, a pair of bevel gears l2, the differential I3, the shaft i4, and the seres.y l5 which engages with suitable teeth at the periphery of the disc 3. The third shaft l of the differential I3 rotates proportionally to the angle of acoustic angular elevation Se, It is connected by the couple 0f bevel gears il to a vertical shaft I8. On this latter shaft there is keyed a cylindrical cam I9 having a groove 20, whose develooment on a plane corresponds to the curve representinnggec Sa as a f unctionoia.

"t one side of the cam I9, there is a strip oi paper 2| which is moved by two rollers 22,n 23, the latter being driven by a motor 3T at a uniform speed. One may give the paper 2l four i to the observation point for a supposed altitude different speeds by means of a speed-change mechanism, which may be` constructed and operated precisely like the change-speed gears of an automobile.

In Athe groove of the cam i9 there is engaged one end of a follower bar 44 which is connected to the last articulation of a Nuremberg chain 45. At the other intersections of theelements of this chain there are articulated by one end three other bars 4S to 48 which are oriented, like the bar 44, transversely to the direction of displacement of the record strip 2l. Toward their other end the bars 44,- 4S, 41 and 48 each bear a sliding block 50 equipped with a stylus or with a tracing roller. These blocks are slidingly mounted on a common vertical rod 5| having at its upper end a horizontal arm 52 which engages the slot in the arm 2 andthe spiral groove 4 in the disc 3. The operator adjusts the angle a in' such a way that .the styli shall be brought as far to the left as possible on the record strip. If the commencement of the lines traced by the styli is oriented approximately at the speed of the strip is suitable and corresponds to the greatest sensitivity of the determination. If not, the operator increases the speed itthe tracing is too nearly horizontal, or decreases it if the tracing is too nearly vertical.

The disc 3 and the sliding crank 2 displace the styli transversely to the record strip according to:

Xa=cot Sa cos (Ga-a) This movement is given to the blocks on which the styli are mounted by the rod 5| whose lateral displacement is made proportional to the cosine of the angle Gra-r` by its engagement with the crank 2, and proportional to cotangent Sa by its engagement with the groove 4 in the disc 3, be-

cause the relative movement of the crank and disc Y is proportional to Sa so that the distance of the cross-piece 52 from the axis of the shaft l is pro-f mentary movement introduces into the tracing the time 0 of transit of the sound of the airplane Z, for

Z cosec Sa where v is the speed of sound in the air.

With the four styli that are illustrated and the four speeds provided for the record strip, one is able to cover the following scales of altitudes:

The relative precision of the determination increases rapidly with the duration of the recording and with the actual speed of the airplane.

For an airplane flying at 10i meters per second at least, if one effects the determination after passage of the airplane to the point that is closest to the listening station, one is able to attain a precision greater than ten per cent.

Of course the invention is not limited to that which has been described and illustrated, but may have various modified forms. Thus, the

Nuremberg chain connecting` the stylus-carrying bars might be replaced by a series of gear-wheels of different diameters, carried by one and the same shaft and engaging with racks, each of which is integral with one of the sty1us-carrying y plane a family of curves representing asa function of time one and the same rectangular coordinate of a horizontal projection of the airplane for different assumed values attributed to the altitude, and selecting the one of these curves which most closely approximates a straight line to ascertain which of the assumed values is the closest to the real altitude.

2. A device for use in determining the altitude of an airplane from the angular elevation and angular bearing of sound coming from` the airplane, which comprises a recording strip, means for moving the recording strip longitudinally at a constant speed, a plurality of styli engaging the recording strip, two input shafts, a common means for moving all the styli across the recording strip, a connection between said means and the two input shafts so arranged that the transverse movement given to the styli is proportional to the cosine of the turning movement given to one of the input shafts multiplied by the cotangent of the turning movement given to the second inp it shaft, separate .means for moving each one of the styli lengthwise of the strip, a connection between the ylengthwise moving means of one stylus and the second input shaft arranged to give this stylus movement lengthwise of the Strip proportional to the cosecant of the turning movement of the second shaft, and a connection between this moving means and the separate moving means of the other Styli arranged to make the lengthwise movements of ythe other styli fixed fractions of the lengthwise movement of the rst stylus, so that when the rst input is given a turning movement proportional to the acoustic bearing angle of an airplane and the second input shaft is given a turning movement proportional to the acoustic elevation angle of the airplane the longitudinal movement of the one of the Styli which traces a straight line on the recording strip indicates the altitude of the airplane.

3. A device for use in determining the altitude of an airplane from the angular elevation and angular bearing of sound .coming from the airplane, which comprises a recording strip, means for moving the recording strip longitudinally at a consta-nt speed. a plurality of styli engaging the recording strip, a plurality of separate blocks on which the styli are mounted, a common transversely movable rod extending lengthwise of the recording strip and slidably engaging al1 said blocks, a plurality of individual rods perpendicular to said rod extending' across ing strip and each engaging one of the stylus blocks` a Nuremberg chain connecting said last-mentioned rods, two input shafts, a. slotted crank connected to one input shaft, a disc containing a spiral groove connected to the other input shaft, an arm on said common rod extending through the slot in the crank and the slot in the disc, a cam connected to the the recordy rality of styli engaging the recording strip, twoinput shafts, commonk means for moving all the styli across the recording strip, connections between said means and the two input shafts, separate means for moving each one of the styli lengthwise of the strip, a connection between the lengthwise moving means of one of said styli and the second input shaft, a connection between this moving means and the separate moving means of the other styl such that they are given lengthwise movements which are fixed fractions of the lengthwise movement of the rst stylus, a constant-speed motor, and change-speed gearing connecting the constant-speed motor with the recording strip so that the speed of the recording strip may be changed to change the inclination of the lines traced by the styli.

` of an airplane from the `angular elevation and i angular bearing ef sound coming from the air 5. A device for use in determining the altitude plane, comprising first and second input shafts,

two shafts connected to one of the input' shafts through a differential so that the turning movement given to the input shaft is equal to the sum of the turning movements of said two shafts, a recording strip moved lengthwise at constant speed, a plurality `of styli engaging the recording strip, a common means for moving all the styli stylus lengthwise of the strip, and a connection between this stylus and the other styli arranged to give'the other styli lengthwise movements which are xed fractions of the lengthwise movement of the first stylus.

ANTONIN SVOBODA. 

